1. Field of the Invention
This invention relates to a coating composition for roof shingles. More particularly, the invention relates to a coating composition for the headlap section of roof shingles.
2. Reported Developments
Roof shingles have to satisfy function, durability and aesthetic appeal. They also have to be inexpensive in order to be marketable. The prior art had addressed these requirements such as disclosed in U.S. Pat. Nos. 4,128,438; 4,274,243; 4,359,505; and 4,378,408.
Roof shingles are intended to provide shelter for the underlying roof structure from precipitation, wind, cold and sun rays, i.e. the roof shingles must be weatherproof and remain so for an extended time period. The roof shingles must also present an aesthetically pleasing feature covering the underlying roof structure. These requirements must be satisfied using inexpensive raw materials.
Roof shingles are typically coated with granules. The granules are generally embedded in the asphalt coating on the surface of an asphalt impregnated felt base material, the granules thus forming a coating that provides an adherent, weather-resistant exterior roofing surface. As the granule coating also provides the aesthetic effect observable with respect to the roofing composition, the appearance of the granules is of major marketing interest. For this reason a pigmented color coat is typically applied to the base mineral granules to enhance their visual, decorative effect. Alternatively, natural crushed stone aggregates have been used instead of the artificially colored granules. This approach has resulted in substantial cost savings.
The present invention is directed to compositions using crushed stone aggregates. More particularly, the present invention is directed to compositions comprising crushed stone aggregates for coating the headlap portion of roof shingles.
The prior art has used natural crushed stone aggregates to which a hydrocarbon oil is applied to control dust. This crushed stone aggregate, being less expensive than artificially colored granules, was applied to the headlap portion of the shingles during the manufacturing process. Although natural headlap granules are inexpensive, more extensive use of them is limited by the fact that they are not as dark or uniform in appearance as desired. For that reason, many shingle manufacturers utilize coal slag or other dark waste aggregate for manufacturing headlap. Furthermore, in order to improve the appearance of natural headlap, efforts have been made to induce a darker color. Thus carbon black has been incorporated in the hydrocarbon oil that was applied to control dust. Darkening of the aggregate results when the hydrocarbon oil deposits carbon black particles within the rock pores as the oil is absorbed into the rock surface. Although effective for pigmentation, the carbon black has poor weathering resistance since it is not strongly bonded to the rock surface and is lost within a few months of weathering exposure.
It has now been surprisingly discovered during weathering studies that pigmentation retention of natural headlap darkened with a hydrocarbon oil/carbon black mixture can be significantly improved by incorporating certain organosilicon compounds in the mixture. The critical requirements in the organosilicon compounds include:
availability of alkoxy or other hydrolizable functional groups to allow bonding with the silanol surface of the rock aggregates;
availability of alkyl or other oleophilic groups that strongly interact with the surface of the carbon black particles; and
complete oil miscibility.
In accordance with the present invention there is provided a composition for application to a headlap comprising per ton of granules:
of from about 1.0 to about 2.5 gallons of a hydrocarbon oil/boiled linseed oil mixture in which the proportion of boiled linseed oil ranges of from about 25% to about 50%;
of from about 0.5 to about 2.0 pounds of powdered or beaded fine particle size carbon black; and
of from about 0.25 to about 1.0 pound of an organosilicon compound.
The process of manufacturing comprises the steps of:
preparing the process oil/boiled linseed oil/organosilicon compound mixture;
heating the mixture from 90-110xc2x0 F. to reduce viscosity to aid carbon black incorporation and to improve rock pore penetration;
mixing a powdered or beaded fine particle sized carbon black with the mixture above to form a homogeneous suspension;
adding this oil/carbon black mixture to the natural headlap granules or colored waste granules in a rotary mixer.
The organosilicon compounds are monomeric silanes having the formula I: 
wherein
R is a large organic group, and preferably a long-chain alkyl group of 6 or more carbons, and most preferably, a long-chain alkyl group of 8-28 carbons;
Rxe2x80x2 is lower alkyl having 1 to 6 carbons, and preferably 1 to 3 carbons, so that the alkoxy functionality is readily hydrolizable and siloxane bond formation with the rock substrate will be rapid; and
n is 1-3, and preferably 1.
Examplary compounds which are also commercially available are as shown in Table A.
Preferably, the organosilicon compounds are siloxane polymers of two or more silane units having the desired functional group characteristics. Examples of commercially available polymeric siloxanes are shown in Table B.